1. Field of the Invention
The present invention relates in general to transducers, and more particularly to acoustic transducers. The present invention also relates to a transducer capable of radiating acoustic energy over a wide band of frequencies. More particularly, the present invention relates to a multiply resonant acoustic transducer with reduced cancellation below the fundamental resonance and improved output performance.
2. Background Discussion
Normally electro-acoustic underwater transducers operate in the vicinity of the fundamental resonant frequency. Maximum output is obtained at the resonant frequency; however, operation in the vicinity of this frequency limits the bandwidth of the transducer. Wideband performance can be obtained above resonance, but the band is often limited by the next overtone resonance. Because of phase shifts, the presence of this overtone resonance generally creates a cancellation between the two resonant frequencies typically resulting in a significant reduction, or notch, in the level of the response, thus limiting the bandwidth.
In our earlier invention, Butler and Butler, “Multiply Resonant Wideband Transducer Apparatus,” U.S. Pat. No. 6,950,373 B2, issued on Sep. 27, 2005, a means is provided for attaining a wide bandwidth above the fundamental resonance through addition in the response between the fundamental and overtone resonant frequencies. Although the invention has been successful, output power in the vicinity of and below the fundamental resonance is limited because a significant portion of the transducer is inactive.
An object of the present invention is to provide additional electro-mechanical-drive active area that still allows the excitation of consecutive modes, but also provides greater output at and below the fundamental resonance.
Another object of the present invention is to provide a voltage stepping means for controlling the strength ratio of the symmetric and anti-symmetric modes without using feedback.